Lignocellulosic materials are the most abundant biomass on earth. It can be converted to simple sugars and other useful products. One example of a potential product is bioethanol, which can be used as an alternative renewable fuel. An effective and environment-friendly approach of converting lignocellulosic materials involves the usage of cellulase enzymes, which catalyze the hydrolysis reactions of the polymeric lignocellulosic materials. However, microbial production of cellulase is regulated by complex gene-level induction and repression mechanisms. This complex regulation causes the production process to be expensive and difficult to operate and/or control. For example, currently the most commonly used inducing substrate is lactose, a disaccharide of glucose and galactose. When added at low concentrations, the inducing efficiency of lactose is sub-optimal. When added at slightly higher concentrations, the glucose formed by the hydrolysis of lactose starts to repress the expression of cellulase genes. That is, the glucose slows or stops the continual synthesis of cellulase.
It is known that the glucose repression occurs at low glucose concentrations. Lactose-based production is therefore hard to control. The difficulties of lactose-based production of cellulase prompted the development of genetically engineered microorganisms to be used for industrial cellulase production. This approach carries serious ecological and environmental risks. Plants rely on the difficulty of cellulase hydrolysis as their first line of defense for microbial attacks.
To meet the possible energy demand from biomass-derived fuel, the industrial biomass conversion will have to occur in very large scales and at widespread production and/or processing sites. Accidental release of large quantities of the genetically engineered microorganisms from these processes could possibly occur. The ecological and environmental effects of the release are unknown but potentially disastrous because a widespread increase in microbial ability of cellulase production may have seriously damaging effects on all plants. A problem is therefore that the use of genetically engineered microorganisms can result in serious ecological and environmental risks.
Sophorose is known to be another inducer for cellulase synthesis. However, its usage in industrial cellulase production has so far been considered infeasible because of its extremely high price. Sophorolipids are glycolipids produced by some yeasts. The various processes for sophorolipid production have been studied and reported.
Earlier work in the field has shown sophorose as an acceptable inducer of cellulase protein but commercialization proves impractical due to cost. See Hrmova, M., Petrakova, E., Biely, P., Journal of General Microbiology 137, 541-547 (1991). In another filing Gross et al. disclosed the use of sophorolipids for protein production. In WO2007/073371, Gross et al., detail the synthesis of sophorlipids with protein inducer and/or repressor activities by fermenting Candida bombicola in a fermentation medium to form a mixture of lactonic and non-lactonic sophorolipids. Again the drawback to this method involves the costs associated with collection, separation and potentially purification of the sophorolipids produced.
Therefore, processes for cellulase production that are effective and economical, as well as those which circumvent complex regulation and use non-genetically-engineered microorganisms, are therefore desirable to the biomass conversion and utilization industry.